Method of adjusting characteristics of a clutch in a hybrid electric vehicle

ABSTRACT

A method of adjusting the characteristics of a clutch in a hybrid electric vehicle, more particularly to a method of adjusting characteristic of a clutch for a hybrid electric vehicle, which is capable of maintaining the characteristic of the clutch at an appropriate level while suppressing the frequency of the adjustment as possible, thereby a driver or passengers of the vehicle hardly feel annoyance caused by frequent adjustment of characteristic of a clutch.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of KoreanPatent Application No. 10-2008-0107791 filed on Oct. 31, 2008, theentire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a method of adjusting thecharacteristics of a clutch in a hybrid electric vehicle, which iscapable of maintaining the characteristics of the clutch at anappropriate level while reducing the frequency of the adjustment of theclutch characteristics, thereby resolving annoyance a driver orpassengers may feel when the adjustment is frequently made.

(b) Background Art

A hybrid vehicle basically refers to a vehicle that uses two or morepower sources to propel the vehicle in a fuel-efficient manner. Mostly,the term ‘hybrid vehicle’ is used for denoting a hybrid electric vehicle(HEV) that includes an internal combustion engine powered by fuel and anelectric motor powered by a battery.

The hybrid vehicle is driven by using electric energy from the batteryand mechanical energy from the engine. In the hybrid vehicle, both theelectric motor and the engine may be operated optimally and regenerativebraking may be employed as well. Accordingly, high energy efficiency canbe achieved.

FIG. 1 schematically illustrates a powertrain (drivetrain) of a parallelhybrid vehicle. The parallel hybrid vehicle comprises an engine 10 as apower source, a motor-generator (MG) 20, a clutch 12 situated betweenthe engine 10 and the motor-generator 20, and an automatic transmission30 to which the output end of the motor-generator 20 is coupled.

The parallel hybrid vehicle is driven in three driving modes: HEV mode,EG mode and EV mode. In HEV mode, both the engine 10 and themotor-generator 20 are used in combination to propel the vehicle. In EGmode, only power from the engine is used. In EV mode, only power fromthe motor-generator 20 is used. The driving mode can be selectedaccording to operation (engagement/disengagement) of the clutch 12,which is controlled by, e.g., a hydraulic device. Namely, the clutch 12is engaged (closed) in EG mode and HEV mode while it is disengaged(opened) in EV mode.

In practical, during low speed driving or at starting of the vehicle,the motor-generator 20, which exhibits maximum torque at low RPM, isused to drive the vehicle When the vehicle enters into steady speedcruising state, the engine 10 is started by means of an integratedstarter/generator (ISG) 40 so that the outputs from the engine 10 andthe motor-generator 20 can be utilized in a combined manner. The outputsfrom the engine 10 and the motor-generator 20 are transmitted to theautomatic transmission 30, which then provides desired rotation speed todriven wheels through a drive shaft 50.

More specifically, during low speed driving or at starting of thevehicle, the clutch 12 is disengaged and the motor-generator 20 thusbecomes a sole power source to drive the vehicle. Since engine torque isminimal at low RPM while motor-generator torque is maximal at low RPM,fuel efficiency can be improved by using the motor-generator 20 tocomplement the torque of the engine 10 at low RPM.

When a driving mode is changed from EV mode to EG or HEV mode, i.e. asthe clutch 12 become engaged, awkward clutch engagement may often occurwith undesirable shock if clutch control is performed withoutconsidering the characteristics of the clutch 12 such as thrust againsta clutch disc, slip rate, torque transmission, relationship betweentemperature and kinds of oil.

Japanese Patent No. 3657902 discloses a method for controlling theoperation of a clutch in a hybrid vehicle by feedback control. Themethod, however, involves undesirable vibration occurring during clutchengagement. Further, Japanese Patent No. 3657902 discloses a method oflearning and adjusting the characteristics of a clutch when clutch slipis available such as in the event of vehicle deceleration. Theadjustment, however, is still insufficient.

On the other hand, Korean Patent Application No. 10-2007-0128676 filedby the present inventors discloses a method of adjusting thecharacteristics of a clutch in a hybrid vehicle, which comprises:idle-rotating the engine by transmitting power from the motor-generatorwith the clutch in half-clutch state in a state where an output to thetransmission is blocked and the engine is in a fuel-cut state;estimating a clutch transmitting torque based on the torque of themotor-generator when rotating speeds of the engine and themotor-generator become constant; and adjusting the characteristics ofthe clutch based on the estimated clutch transmitting torque. Thismethod, still, can be applied only when the transmission is in neutral(non operation) state. For this reason, it is hard to perform suchadjustment frequently.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

In a preferred embodiment, the present invention provides a method ofadjusting characteristic data of a clutch for a hybrid electric vehicle.The hybrid electric vehicle may include: a motor-generator, a rotationalspeed detecting means thereof, a suitable control means thereof, and anestimating means for output torque thereof; an engine, a rotation speeddetecting means thereof, and a control means thereof; a clutchinterposed between the motor-generator and the engine, and a clutchcontrol means for controlling the clutch such that power transmissionbetween the engine and the motor-generator is suitably controlled; atransmission for transmitting, blocking or converting power from themotor-generator and/or the engine to driven wheels, and a control meansthereof; an estimating means for clutch transmitting torque; and aplurality of characteristic maps of clutch transmitting torque forcontrol. The method may comprise steps of: estimating a clutchtransmitting torque by a first clutch transmitting torque estimatinglogic when ignition is ON, after confirming a vehicle is in a state ofbraking and the transmission is configured to transmit power from aninput to the driven wheels; checking an error between the clutchtransmitting torque estimated by the first clutch transmitting torqueestimating logic and clutch characteristic data obtained from thecharacteristic maps of clutch transmitting torque for control;terminating further procedures in case where the error is within apredetermined range; estimating a clutch transmitting torque by a secondclutch transmitting torque estimating logic in case where the errorexceeds the predetermined range, the second clutch transmitting torqueestimating logic being configured to estimate a clutch transmittingtorque based on torque of the motor-generator; and adjusting the clutchcharacteristic data in accordance with the clutch transmitting torqueestimated by the second clutch transmitting torque estimating logic.

Suitably, the first clutch transmitting torque estimating logic mayestimate an engine friction torque as a clutch transmitting torque whena rotation speed of the engine becomes constant, i.e. aftersynchronization of the engine friction torque and the clutchtransmitting torque.

Suitably, the clutch characteristic data may be a predicted clutchtransmitting torque that is read out from the characteristic maps ofclutch transmitting torque for control in accordance with a clutchcontrol pressure and difference of rotation between the engine and themotor-generator at time of the estimation of clutch transmitting torque.

Preferably, the clutch transmitting torque estimated by the secondclutch transmitting torque estimating logic my be identical with thetorque of the motor-generator, whereby the clutch characteristic data isadjusted based on the torque of the motor-generator.

Preferably, the step of adjusting the clutch characteristic data maycomprise selecting one as a control map from the pre-registeredplurality of characteristic maps of clutch transmitting torque, based onthe clutch transmitting torque estimated by the second clutchtransmitting torque estimating logic and difference in rotation betweenthe engine and the motor-generator at time of the estimation of clutchtransmitting torque.

Preferably, a characteristic map that has the closest torque to theclutch transmitting torque at difference of rotation between the engineand the motor-generator may be selected as the control map.

Suitably, the method may further comprise steps of: repeating estimationof a clutch transmitting torque by the first clutch transmitting torqueestimating logic and check of an error between the estimated clutchtransmitting torque and clutch characteristic data whenever ignition isON; and determining abnormality of the clutch characteristic data if anumber of errors exceeding the predetermined range reaches a thresholdvalue within predetermined times.

Suitably, The method may further comprise steps of: repeating estimationof a clutch transmitting torque by the first clutch transmitting torqueestimating logic and check of an error between the estimated clutchtransmitting torque and clutch characteristic data whenever ignition isON; adjusting the clutch characteristic data in accordance with theclutch transmitting torque estimated by the second clutch transmittingtorque estimating logic in case where a number of errors being withinthe predetermined range reaches a threshold value; estimating a clutchtransmitting torque by the first clutch transmitting torque estimatinglogic; checking an error between the estimated clutch transmittingtorque and clutch characteristic data; and determining abnormality oferror checking procedure itself or the clutch if the error exceeds thepredetermined range.

Other aspects and features of the invention are discussed in detailinfra.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircrafts, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be describedin detail with reference to certain exemplary embodiments thereofillustrated by the accompanying drawings which are given hereinafter byway of illustration only, and thus are not limitative of the presentinvention, and wherein:

FIG. 1 schematically illustrates a drive system and a powertrain(drivetrain) of a parallel hybrid vehicle;

FIG. 2 is a schematic diagram showing a method of adjusting thecharacteristics of a clutch in a hybrid electric vehicle according to anembodiment of the present invention;

FIG. 3 is a flow chart showing a process of estimating a clutchtransmitting torque by a first clutch transmitting torque estimatinglogic and checking an error by comparing the estimated clutchtransmitting torque with a clutch characteristic data for controlaccording to an embodiment of the present invention;

FIG. 4 is a schematic diagram showing an operation of a hybridpowertrain when a clutch transmitting torque is estimated by a firstclutch transmitting torque estimating logic according to an embodimentof the present invention;

FIG. 5 is a schematic diagram showing an operation of a powertrain whena clutch transmitting torque is estimated by a second clutchtransmitting torque estimating logic according to an embodiment of thepresent invention;

FIG. 6 is a flow chart showing a process of estimating a clutchtransmitting torque by a second clutch transmitting torque estimatinglogic and adjusting the clutch characteristics data according to anembodiment of the present invention;

FIG. 7 is a graph illustrating a plurality of pre-registeredcharacteristics maps from a control map is selected based on anestimated clutch transmitting torque; and

FIG. 8 is a graph illustrating a time-lag in accelerating a vehicleleading to feeling of incongruity.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the drawings attachedhereinafter, wherein like reference numerals refer to like elementsthroughout. The embodiments are described below so as to explain thepresent invention by referring to the figures.

The present invention provides a method of adjusting the characteristicsof a clutch in a hybrid electric vehicle, which is capable ofmaintaining the characteristics of the clutch at an appropriate levelwhile reducing the frequency of the adjustment.

In an embodiment of the present invention, a powertrain (drivetrain) ofa hybrid vehicle comprises: a motor-generator, a rotational speeddetecting means thereof, a control means thereof, and an estimatingmeans for output torque thereof; an engine, a rotation speed detectingmeans thereof, and a control means thereof; a clutch interposed betweenthe motor-generator and the engine, and a clutch control means forcontrolling the clutch such that power transmission between the engineand the motor-generator is suitably controlled; a transmission fortransmitting, blocking or converting power from the motor-generatorand/or the engine to driven wheels, and a control means thereof; anestimating means for clutch transmitting torque; and a plurality ofcharacteristic maps of clutch transmitting torque for control.

Referring to FIG. 2, according to a method of according to an embodimentof the present invention, in step a, every time the vehicle is driven(e.g., ignition ON), the characteristics of a clutch of a vehicle aredetermined at the deceleration of the vehicle the by a method that isapplicable to a vehicle in deceleration state.

In step b, an error is then determined by comparing the determinedcharacteristics of the clutch with a clutch characteristics data forcontrol.

In step c, if the determined error is within a predetermined range(i.e., OK state), the determined characteristics of the clutch are usedas data for generating control signal; on the other hand, if thedetermined error is out of the predetermined range, the characteristicsof the clutch are estimated by a method as detailed below and on thebasis of the estimated characteristics of the clutch, the clutchcharacteristics data for control is renewed and utilized as data forgenerating control signal.

In step d, if the error still is out of the predetermined range evenafter repeating the steps a and b (i.e. NG state), the step c isrepeated. During the repetition, if a predetermined number (e.g. 10 or20) or higher of the NG state is consecutively detected, a warning fordeterioration of the characteristics of the clutch is issued.

In step e, if a predetermined number (e.g. 10 or 20) or higher of the OKstate is detected consecutively, the steps c and d are forciblyperformed to self-diagnose whether the steps a, b, and c are properlyperformed.

Hereinafter, the method of adjusting the characteristics data of aclutch in a hybrid vehicle will be described in detail.

1) Normal Control Procedure

When a vehicle is in ignition ON state, a first clutch transmittingtorque estimating logic checks whether the transmission is in D-rangeand the vehicle is decelerating. If it is determined that thetransmission is in D-range and the vehicle is decelerating, the firstclutch transmitting torque estimating logic checks an error by comparingthe estimated clutch characteristics in the step a with a clutchcharacteristics data for control. If the error lies within apredetermined range, no further procedure is performed.

With reference to FIGS. 3 and 4, the above-mentioned error checkingprocess is explained in detail.

When a vehicle is decelerating with the transmission in D-range, controlpressure of the clutch is increased and rotation of the wheels istransferred to the engine. At this time, the engine, in a fuel-cutstate, absorbs a clutch transmitting torque by engine friction.

The rotation speed of the engine becomes constant as the clutchtransmitting torque and the engine friction torque are synchronized witheach other. The engine friction torque at this time point ofsynchronization is deemed as an estimated clutch transmitting torque.Based on the estimated clutch transmitting torque, clutchcharacteristics data for control is checked.

The clutch characteristics data for control is checked by comparing theestimated clutch transmitting torque with a predicted clutchtransmitting torque, The predicted clutch transmitting torque is readout from a characteristics map of clutch transmitting torque forcontrol, based on a clutch control pressure and a difference between theengine rotation speed and the motor-generator rotation speed at the timepoint of the synchronization.

If |the estimated clutch transmitting torque—the predicted clutchtransmitting torque| is lower than a predetermined value (i.e., OKstate), no further procedure is performed. The predetermined value issuitably obtained in advance from empirical data of an actual vehicletest. On the other hand, if |the estimated clutch transmittingtorque—the predicted clutch transmitting torque| is the same as orhigher than the predetermined value (i.e., NG state), a second clutchtransmitting torque estimating logic is executed.

The second clutch transmitting torque estimating logic serves toestimate a clutch transmitting torque. Based on the estimated clutchtransmitting torque, adjustment of the clutch characteristics data forcontrol is performed. Such adjustment of the clutch characteristics datafor control is performed by a method as described below.

With reference to FIGS. 5 and 6, with the transmission 30 in P or Nrange, the motor-generator 20 is rotated by means of power transferredfrom the engine 10 through the clutch 12 in half-clutch state. It isdetermined by the second clutch transmitting torque estimating logicwhether the rotation speeds of the engine 10 and the motor-generator 20become stable (i.e., steady state). The motor-generator torque at thesteady state is estimated as a clutch transmitting torque. The clutchcharacteristics are adjusted based on the estimated clutch transmittingtorque.

More specifically, with the transmission 30 set to non-driving state, anISG 40 starts the engine 10. The torque generated by the engine 10 istransmitted to rotate the motor-generator 20 via the clutch 12 inhalf-clutch state.

The motor-generator 20 is controlled in such a manner that the rotationspeed thereof becomes constant by absorbing the engine torque. Therotations of the engine and the motor-generator become steady when theengine output torque, the clutch transmitting torque, and themotor-generator torque are synchronized together. The motor-generatortorque at the steady state is deemed as an estimated clutch transmittingtorque. From a plurality of candidate characteristics maps of clutchtransmitting torque for control, a map closest to the slip rotation(rotation rate) corresponding to the estimated clutch transmittingtorque is selected.

More particularly, as shown in FIG. 6, the duty of the clutch controlpressure is set by a predetermined duty value and the rotation speed ofthe motor-generator is set by a predetermined target rotation speed.Whether a difference between the (real) rotation speed of themotor-generator and the predetermined target rotation speed lies in aallowable clearance; whether fluctuation of the rotation speed of theengine lies in a allowable clearance; and whether fluctuation of therotation speed of the motor-generator lies in a allowable clearance aredetermined. If it is determined that the difference and fluctuations arewithin respective clearances, rotation speeds of the engine andmotor-generator become steady. The torque of the motor-generator at thesteady state is estimated as a clutch transmitting torque. Based on theestimated clutch transmitting torque, the characteristics of the clutchare adjusted.

The clutch characteristics adjustment may be made by using a control mapselected from a plurality of candidate characteristics maps on the basisof the estimated clutch transmitting torque and a difference between therotation speeds of the engine and the motor-generator corresponding tothe estimated clutch transmitting torque. Also, the clutchcharacteristics adjustment may be made by using a map selected from aplurality of candidate characteristics maps on the basis of real clutchtransmitting torque measured and a difference between the rotationspeeds of the engine and the motor-generator corresponding to themeasured real clutch transmitting torque.

FIG. 7 illustrates a plurality of pre-registered characteristics mapsfrom which a control map is selected based on the real clutchtransmitting torque. As shown in the figure, the map 1 that has a torqueclosest to a real clutch transmitting torque is selected as a controlmap.

Upon completion of the adjustment for the characteristics data of theclutch for control by the second clutch transmitting torque estimatinglogic, an error check for the characteristics data of the clutch forcontrol is performed again by the first clutch transmitting torqueestimating logic. If the error lies within a predetermined range, nofurther procedure is performed. Otherwise, adjustment for thecharacteristics data of the clutch by the second clutch transmittingtorque estimating logic is repeated and such an error check is repeated.Upon the error check, if the error is within the predetermined range, nofurther procedure is performed. On the other hand, if the error is stillout of the predetermined range, it is determined that the error checkinglogic(s) or the clutch itself is out of order and the characteristicsdata of the clutch for control is then replaced with a characteristicsdata of the clutch for fail (emergency).

2) Detection for Abnormality of the Characteristics Data of the Clutch

As described in the foregoing procedure 1), the first clutchtransmitting torque estimating logic checks an error of a clutchcharacteristics data for control, and if the error lies within apredetermined range, the procedure 1) is terminated. Here, terminationof the procedure 1) also occurs when the error lies within thepredetermined range in further error checks done after adjustment of thecharacteristics data of the clutch by the second clutch transmittingtorque estimating logic.

The error check is performed repeatedly whenever ignition is ON. If theerror is detected to be out of the predetermined range for apredetermined number of times (e.g., 3 times), it is determined that thecharacteristics data of the clutch does not accord with normal variationof a typical characteristics data of the clutch (i.e. in abnormalstate), and then the characteristics data is replaced with acharacteristics data for a failure situation. Suitably, thepredetermined number is obtained from empirical data of a actual vehicletest.

3) Detection for Abnormality of Error Checking

As described in the foregoing procedure of 1), the first clutchtransmitting torque estimating logic checks an error of a clutchcharacteristic data for control, and if the error lies within apredetermined range, the procedure 1) is terminated. Here, terminationof the procedure 1) also occurs when the error lies within thepredetermined range in further error checks done after adjustment forthe characteristic data of the clutch by the second clutch transmittingtorque estimating logic.

The error check is performed repeatedly whenever ignition is ON. If theerror is detected to be within a predetermined range for at least apredetermined number of times (e.g., 20 times) consecutively, thecharacteristics data of the clutch is adjusted using the second clutchtransmitting torque estimating logic.

Subsequently, the first clutch transmitting torque estimating logicchecks an error of the adjusted clutch characteristics data for control,and if the error lies within a predetermined range, no further procedureis performed. On the other hand, if the error is out of thepredetermined range, it is determined that the error checking logic(s)itself is out of order and the characteristics data is replaced with acharacteristic data for a failure situation.

According to the aforementioned methods, the characteristics of a clutchin a hybrid vehicle can be adjusted accurately (approximately, 95% ofaccuracy) and less frequently (e.g., every 5000 km), thereby decreasingthe feeling of incongruity. Also, the clutch characteristics estimationor clutch itself can be monitored so as to immediately detect failurethereof.

Here, the feeling of incongruity indicates time-lag in accelerating. Asshown in FIG. 8, when a driver steps on an accelerating pedal, theestimation procedure is ceased and the transmission is shifted from Nrange to D range in response to the driver's order.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

1. A method of adjusting characteristic data of a clutch for a hybridelectric vehicle, the hybrid electric vehicle including: amotor-generator, a rotational speed detecting means thereof, a suitablecontrol means thereof, and an estimating means for output torquethereof; an engine, a rotation speed detecting means thereof, and acontrol means thereof; a clutch interposed between the motor-generatorand the engine, and a clutch control means for controlling the clutchsuch that power transmission between the engine and the motor-generatoris suitably controlled; a transmission for transmitting, blocking orconverting power from the motor-generator and/or the engine to drivenwheels, and a control means thereof; an estimating means for clutchtransmitting torque; and a plurality of characteristic maps of clutchtransmitting torque for control, the method comprising steps of:estimating a clutch transmitting torque by a first clutch transmittingtorque estimating logic when ignition is ON, after confirming a vehicleis in a state of braking and the transmission is configured to transmitpower from an input to the driven wheels; checking an error between theclutch transmitting torque estimated by the first clutch transmittingtorque estimating logic and clutch characteristic data obtained from thecharacteristic maps of clutch transmitting torque for control;terminating further procedures in case where the error is within apredetermined range; estimating a clutch transmitting torque by a secondclutch transmitting torque estimating logic in case where the errorexceeds the predetermined range, the second clutch transmitting torqueestimating logic being configured to estimate a clutch transmittingtorque based on torque of the motor-generator; and adjusting the clutchcharacteristic data in accordance with the clutch transmitting torqueestimated by the second clutch transmitting torque estimating logic. 2.The method according to claim 1, wherein the first clutch transmittingtorque estimating logic estimates an engine friction torque as a clutchtransmitting torque when a rotation speed of the engine becomesconstant, i.e. after synchronization of the engine friction torque andthe clutch transmitting torque.
 3. The method according to claim 1,wherein the clutch characteristic data is a predicted clutchtransmitting torque that is read out from the characteristic maps ofclutch transmitting torque for control in accordance with a clutchcontrol pressure and difference of rotation between the engine and themotor-generator at time of the estimation of clutch transmitting torque.4. The method according to claim 1, wherein the clutch transmittingtorque estimated by the second clutch transmitting torque estimatinglogic is identical with the torque of the motor-generator, whereby theclutch characteristic data is adjusted based on the torque of themotor-generator.
 5. The method according to claim 1, wherein the step ofadjusting the clutch characteristic data comprises selecting one as acontrol map from the pre-registered plurality of characteristic maps ofclutch transmitting torque, based on the clutch transmitting torqueestimated by the second clutch transmitting torque estimating logic anddifference of rotation between the engine and the motor-generator attime of the estimation of clutch transmitting torque.
 6. The methodaccording to claim 5, wherein during the selection of the control map, acharacteristic map that has the closest torque to the clutchtransmitting torque at difference of rotation between the engine and themotor-generator, is selected as the control map.
 7. The method accordingto claim 1, further comprising steps of: repeating estimation of aclutch transmitting torque by the first clutch transmitting torqueestimating logic and check of an error between the estimated clutchtransmitting torque and clutch characteristic data whenever ignition isON; and determining abnormality of the clutch characteristic data if anumber of errors exceeding the predetermined range reaches a thresholdvalue within predetermined times.
 8. The method according to claim 1,further comprising steps of: repeating estimation of a clutchtransmitting torque by the first clutch transmitting torque estimatinglogic and check of an error between the estimated clutch transmittingtorque and clutch characteristic data whenever ignition is ON; adjustingthe clutch characteristic data in accordance with the clutchtransmitting torque estimated by the second clutch transmitting torqueestimating logic in case where a number of errors being within thepredetermined range reaches a threshold value; estimating a clutchtransmitting torque by the first clutch transmitting torque estimatinglogic; checking an error between the estimated clutch transmittingtorque and clutch characteristic data; and determining abnormality oferror checking procedure itself or the clutch if the error exceeds thepredetermined range.